The present invention relates to the field of communication systems and, more particularly, to a patch antenna used in spaceborne and phased array antenna systems.
A single linearly-polarized, proximity-fed stacked patch antenna is disclosed in commonly assigned U.S. Pat. No. 5,874,919 to Rawnick et al., the disclosure which is hereby incorporated by reference in its entirety. This stacked patch antenna advantageously provides an active and parasitic patch antenna element having a distributed antenna resonance characteristic. A patch antenna element is secured by conventional pick-and-place techniques on a dielectric substrate having a feed line with a tuning stub. In this design, the antenna is a stub-tuned, proximity-fed, stacked patch antenna configuration having a primary xe2x80x9cactivexe2x80x9d (disk-shaped) patch antenna element and a secondary xe2x80x9cparasiticxe2x80x9d or passive (disk-shaped) patch antenna element of a different size that resonates at respectively different or offset frequencies. The primary or active patch is field-coupled to, rather than pin-fed by, the conductive microstrip feed line formed as a layer on top of the dielectric substrate overlying a ground plane. The structure can define a front face sheet of a panel-configured antenna module.
The microstrip feed line includes an antenna tuning stub formed adjacent to the active patch antenna element that produces an additional resonant frequency in the vicinity of the resonant frequency of the active patch and that of the parasitic/passive patch. The close proximity of the tuning stub to the stacked patch antenna causes electromagnetic field energy associated with the tuning stub to be coupled with the active and parasitic patch antenna elements, causing the patch antenna to exhibit an additional radiating mode, creating a distributed resonance characteristic that is a composite of the three components. It has an augmented bandwidth compared with that of a conventional patch antenna using a pin feed.
Space-qualifiable, pressure-sensitive adhesive material is interleaved among the parasitic patch antenna element, an insulating spacer disk, and the active patch antenna element. The parasitic and active patch antenna elements and insulating spacer disk form a patch antenna element that can be pick-and-placed onto a dielectric substrate and a ground plane-defining front face sheet by methods known to those skilled in the art.
This design provides a single polarization. A need has arisen in the industry for a dual-polarization configuration. A drawback of the system is that the feed mechanism is not amenable to a dual-polarized element design via the standard manufacturing design practice as disclosed within the incorporated by reference ""919 patent, where the feed line extends to the center of the patch. The length of this feed line is critical to antenna element performance. The structure as designed cannot be dual-polarized by adding overlapping feed lines at the center, which would create coupling between the feed lines, and thus, negate the entire function of the patch antenna.
In view of the foregoing background, it is therefore an object of the present invention to provide a stub-tuned, proximity-fed, stacked patch antenna that provides dual polarization.
This and other objects, features and advantages, in accordance with the present invention, are provided by a proximity-fed, stacked patch antenna that includes a ground plane layer and a dielectric substrate overlying the ground plane layer. An active patch antenna element is disposed on the dielectric substrate. A parasitic patch antenna element is supported in spaced relation to the active patch antenna element. Dual feed lines are spaced from and field-coupled to the active patch antenna element. Each feed line has a tuning stub for producing a distributed antenna resonance. The dual feed lines are configured to provide dual polarization and minimize coupling between the two feed lines.
In one aspect of the present invention, each feed line comprises a microstrip feed line formed on the dielectric substrate. In another aspect of the present invention, the feed lines are positioned substantially orthogonal to each other to provide orthogonal linear polarizations. Each feed line includes a feed line tip that extends towards the center of the active patch antenna element, but are spaced from each other to minimize tip-to-tip coupling. Each feed line tip includes a 90 degree bend forming a xe2x80x9cchamferxe2x80x9d bend.
Each tuning stub also has a length of about one-half radius of the active patch antenna element. Each tuning stub can be located adjacent to the outer edge formed by the active patch antenna element. The active and parasitic patch antenna elements are formed of a metallic material, such as a foil disk for the parasitic patch antenna element.
In yet another aspect of the present invention, the active and parasitic patch antenna elements comprise circular disks and have a diameter greater than the diameter of the active patch antenna element. The active patch antenna element has a first resonant frequency and the parasitic antenna element has a second resonant frequency.
In yet another aspect of the present invention, the patch antenna element is formed from the active and parasitic patch antenna elements and adhesively secured onto the dielectric substrate, such as by pick-and-place techniques known to those skilled in the art.
A method of forming a proximity-fed, stacked patch antenna is also disclosed and comprises the step of positioning a patch antenna element formed of an active and parasitic patch antenna element over a dielectric substrate having a conductive feed layer of dual feed lines, such that the patch antenna element is field-coupled to the dual feed lines and configured to provide dual polarization and minimal coupling between the feed lines. The patch antenna element is adhesively adhered to the dielectric substrate.